As a result of the termination of the merger agreement, Aetna will pay Humana $1 billion. Additionally, Aetna has terminated its previously announced agreement to sell certain Medicare Advantage assets to Molina Healthcare and will pay the applicable fees associated with that termination.

Aetna chairman and CEO Mark Bertolini, said: "While we continue to believe that a combined company would create greater value for health care consumers through improved affordability and quality, the current environment makes it too challenging to continue pursuing the transaction."

"We are disappointed to take this course of action after 19 months of planning, but both companies need to move forward with their respective strategies in order to continue to meet member expectations. Our mutual respect for our companies’ capabilities has grown throughout this process, and we remain committed to a shared goal of helping drive the shift to a consumer-centric health care system."